According to the construction of a conventional, known socket for IC package, a large number of contacts are arranged side by side along side portions of an IC package receiving space formed on the upper surface of a base member, the contacts each having a contact portion for contact with a lead of the IC package received in the receiving space and also having a spring portion for biasing the contact portion inwards to obtain contact pressure for the lead, and the contact portion of each contact is displaced outward against the biasing force of the spring portion by depressing a cover which covers the base member, thereby permitting the IC package to be mounted and removed in an unloaded condition (see Japanese Patent Laid Open Nos. 154065/92 and 307678/88).
The applicant in the present case has previously invented and filed an application for a socket for IC package wherein the shape of the spring portion of each contact mentioned above is specified and a projection is formed on the upper surface of the spring portion, while a recess for engagement with the projection is formed in a connection shaft which is supported vertically and pivotably along the row of the contacts. Further, movable cams are supported pivotably on both right and left sides of the contact row and a bearing hole in the shape of an elongated hole or a circular hole for pivotally supporting support portions at both ends of the connection shaft is formed in each of the movable cams. This eliminates drawbacks of the above conventional socket and bring about excellent advantages in all of the contact pressure of the contact portions for the leads of IC package, operating load in depressing the cover, operation life thereof and a sure gripping ability for IC package (see Japanese Patent Application Nos. 104178/93 and 157310/93).
In the foregoing conventional socket and the above socket filed previously by the applicant in the present case, as shown in FIG. 12, a central portion of the upper surface of a base member 100 is used as a receiving space 101 for a package body P1, the receiving space 101 is surrounded with a rib 102, a seating surface 103 for package leads P2 is formed outside the rib 102, and contact portions 301 of contacts 300 are displaced outward by depression of a cover 200 to bring the seating surface 103 into a vacant state for reception of an IC package.
The depressing operation of the cover 200 and the mounting work for the IC package are automated. For the mounting of the package there is adopted a method wherein the package P is carried up to the position just above the receiving space 101 by means of a vacuum chuck for example, and in this state the vacuum is released, thereby allowing the package to drop. After the IC package has thus dropped, the package body P1 is moved into the receiving space 101 while being guided by the positioning rib 102 and a guide slant 201, and when the leads P2 are seated on the seating surface 103, the package body is set on the base member 100.
However, a still more detailed study of the above IC package receiving structure and IC package mounting method shows that there still remains the following problem.
In the structure described above, it is very likely that there will occur tilting of the package at the time of dropping thereof. In this case, the leads (or lead group) P2 on the lower side in the tilting direction are the first to sit on the seating surface 103, so the weight of the package body P1 or a dropping impact is imposed on the leads P2, thus causing deformation and hence providing a defective product.